In my earlier tutorials on photographing wild
birds I have covered points 1 and 2 in my list of common errors:
1) Subject too distant.
2) Subject not in focus
3) Blur due to subject movement - motion blur
4) Blur due to camera movement
5) Incorrect exposure
6) Little consideration given to lighting or composition

Let's now carry on moving down the list and finding counters to
these issues.

3) Blur due to subject movement

Birds are constantly in motion, preening, feeding,
hopping around and flying but small birds in particular are constantly
twitching and making small movements of their head or wings. The
most significant cause of image softness when photographing birds
is caused by insufficient shutterspeed.

To photograph a bird such as this blue tit I would not use less
than 1/250th sec to be sure of freezing the motion. I actually
took this image at 1/750sec at ISO 200 at my 400mm lens's widest
aperture of f5.6 to ensure that it would be sharp.

Such shutterspeeds at low ISO settings are quite easy to achieve
on a sunny day, particularly if you are using the lens at a wide
aperture setting (which lets in more light). However, when the light
conditions are less favourable the shutterspeed can drop away very
quickly and it becomes all too easy to lose critical sharpness.
Under these dull conditions, you can open up the aperture to let
in more light, but you will start to lose depth of field if you
do and may not get all of the intended parts of the subject in focus.
Every stop of aperture will translate into a doubling of shutterspeed,
so 1/125 sec at f8 will become 1/250 sec at the next wider aperture
setting of f5.6.

Next problem is that you will hit the lens's maximum aperture so
you are stuck with the shutterspeed you have. The solution of course
is to increase the camera's ISO setting which increases the camera
sensor's sensitivity to light .A good analogy is to think of it
as a dimmer switch on the lights in your home - wind up the power
(ISO) and generate more light. Every doubling of ISO will double
your shutterspeed, so 1/125 sec at 200 ISO will increase to 1/250th
sec at ISO 400 if you keep the aperture the same. The penalty you
pay for increasing ISO is that you will begin to notice noise creeping
into your images.

Noise is unwanted granularity that is most obvious in the shadow
areas of an image.This is a result of amplifying the signal, (due
to increasing the ISO setting) and in so doing we also amplify the
background electrical noise that is present in the camera's electrical
system. Noise is described as chroma or luminance noise. Chroma
noise looks like irregular blotches of colour and can be fairly
easily removed in noise-reduction editing software .Luminance noise
is a same-colour granularity present in one or more colour channels
and is harder to remove without smearing detail and making the image
look artificial. Luminance noise often turns up in high ISO pictures
containing blue skies. As the blue sky is a continuous area a selection
of it can be made in Photoshop and noise reduction software used
to remove it.The following two shots are huge 200% magnifications
of the background of an image. The 3200 ISO image contains a lot
of chroma noise

ISO 400

ISO 3200

Fortunately the camera manufacturers have made big advances recently
in controlling noise by improved sensor design and by using in-camera
noise reduction algorithms.This means that unlike in the days of
film where grain was very evident in images above ISO ratings of
about 100, in the digital age we have things much easier. These
days some digital SLRs are capable of producing very usable images
up to 3200-6400 ISO. Some can go much higher than this even, despite
cramming increasing numbers of pixels on the sensor. Such images
are often still usable in newspapers or for viewing at small size
on websites, where the quality is not so critical.

We must therefore not be afraid of using high ISO settings when
the need arises. It is better to get a sharp
but grainy image than a blurred grainless one ! There
are some excellent pieces of noise reduction software available
today such as Neat Image and Noise Ninja that reduce noise significantly
without destroying detail if used with care. There is also one other
weapon in our armoury in the fight against noise, which is to ensure
that we don't under-expose the image as we will reveal noise in
the shadows when we brighten-up the image again in post-processing.
This technique is called "exposing
to the right" and is covered by a separate tutorial on
this subject.

I learned a lot about working at balancing shutterspeed and aperture
vs ISO by studying the work of two excellent Finnish Bird Photographers
- Jari Peltomaki and Markus Varesvuo. In Finland, light levels are
often very low - as they are in the UK in winter. If you take a
look at their website there
are lots of images with the exposure information displayed. You
might be surprised at how high their shutterspeeds are on occasion
(1/3200 sec or more), particularly when birds are in flight.They
will often use a high ISO even in bright conditions in exchange
for a combination of high shutterspeed plus a small aperture in
order to get all of their subject in focus. Once you have looked
at some of their images, I suggest you play a game of looking at
a picture and then trying to guess what camera settings they used.
I learned a lot this way and you will probably too.

In the above image, a hawfinch and a female
blackbird are squabbling over a bathing place. I froze the action
with a shutterspeed of 1/500 sec at f6.3. I used an ISO setting
of 800 to achieve this shutterspeed.

In the next image of a hawkowl catching a vole in the snow, I
had to use a shutterspeed of 1/3200 sec at f5.6 to freeze the action
of this lightening fast attack. This demanded an ISO setting of
ISO 1250 to achieve. On the latest generation of cameras I would
have used ISO 3200 without a moments hesitation to get this shot.

The next image of a purple sandpiper is nearly frame-filling so
the magnification is high. I used a narrow aperture to blur the
background but the bird's feet are now out of focus. When magnification
is high like this, you need to stop the lens down more than you
would normally.